Leviticus 11:40

He who eateth of its carcase shall wash his clothes, and be unclean until the evening; and he who carrieth its carcase shall wash his clothes, and be unclean till evening.

The laws of eating are severe, like the laws of carrying, for in fact both carry the carcass — one inside, and one outside.

AND HE THAT EATETH OF THE CARCASS OF IT SHALL WASH HIS CLOTHES, AND BE UNCLEAN UNTIL THE EVEN. In line with the plain meaning of Scripture, the verse speaks here of one who eats in the way that people usually eat, namely, that he touches and carries what he eats, and therefore becomes impure by contact and by carrying. It was necessary to mention this case so that it should not occur to anyone that because of eating, his degree of impurity should be greater [than that resulting merely from contact and carrying]. It mentioned this law in regard to an animal fit for food [as mentioned in the preceding Verse 39], because a person can [easily] err with regard to it, thinking that it was slaughtered properly [and he will therefore eat it], but such errors do not normally occur with regard to forbidden animals, and the way of the Torah is to speak of what usually happens. But according to its [Rabbinic] interpretation, the verse comes to prescribe the [minimum] size required to become impure through carrying or touching, namely an amount that can be called “eating,” which is the size of an olive and Scripture also mentioned this law in regard to carrion of an animal fit for food, whilst the same law applies to an animal not permitted as food, because He finished here the law of impurities. According to the opinion of the interpretation of the Torath Kohanim, 4:2; 10:1-4. all impurities [conveyed] by carrion [of animals fit for food and those which are unfit animals] are included here, and the section above refers to limbs of animals. I have already mentioned this., in Verse 24.

מנבלתה , our sages in Niddah 42 understand the wording as telling us something about the minimum size of the carcass which can confer such ritual impurity. [based on the preposition מ in the word מנבלתה, meaning “part of its carcass.” If one carries a sufficient quantity of such a carcass which would qualify halachically as “food,” i.e. consumption of this quantity of forbidden food would make the party culpable for a penalty, then it confers ritual impurity on the person carrying it. The amount is the equivalent of the size of an olive. According to the plain meaning of the text the meaning is that if one eats of this carcass one become ritually impure even if one never touched any part of it. (compare what the Torah writes in Leviticus 22,8)